I did not find it scary at all...
That is, until, I was made aware of some real life cases...
This is why the movie is scary. If a person doesn't believe in this stuff or has never heard of the real story behind The Exorcist, then it won't be scary for them.
Did anyone hear what happended to The Pope a few months ago? He was at an outdoor blessing and a girl started cursing him and started getting agressive. She was subdued, and after a while she calmed down. The Pope decided to talk to her. He was very suprised to hear her speaking old, dead Latin and some other languages as well. Not the normal Latin which is pretty dead anyway, but even older stuff that The Pope knew. I guess he did try some of the ritual of exorcism on her, but she mocked his feeble attempt at an exorcism. The official story from the Catholic Church was that he only prayed with her for a while.
I also heard that the Vatican has one of, if not the largest language databases on the planet. They can record someone talking and the computers can figure out what language they speak. The results from this girl were amazing. She was speaking at least 6 different languages and they could only recognize 4 of them.
Father Gabriel Amorth, the head Exorcist in Rome, had tried an exorcism on the girl a while before, but it didn't work. For some perspective, he has been involved in thousands of exorcisms. He has a book called " An Exorcist Tells His Story", but it's not the sensational book that most people are looking for.